Gaseous alternative fuels, such as hydrogen and natural gas, are valued for their clean burning characteristics in motor vehicle engines. However, the volume and weight of fuel storage tanks for gaseous alternative fuel are large, compared to petroleum or liquid alternative fuel storage tanks for equal vehicle driving range. One way to overcome this limitation is to refrigerate the gases until they become cryogenic liquids. High-density cryogenic storage tanks are called “dewars”.
A particularly clean burning gaseous alternative fuel known as known as HYTHANE is formed from a mixture of hydrogen and natural gas. The prefix “Hy” in HYTHANE is taken from hydrogen. The suffix “thane” in HYTHANE is taken from methane, which is the primary constituent of natural gas. HYTHANE can be supplied to internal combustion engines from homogeneous compressed gas mixtures stored on board the vehicle in high-pressure fuel tanks. U.S. Pat. No. 5,139,002 to Frank E. Lynch and Roger W. Marmaro describes the production and use of HYTHANE in internal combustion engines. The '002 patent prescribes mixtures in the range of 10-30 percent hydrogen by volume in methane for various applications.
Unlike hydrogen and methane from which HYTHANE is made, HYTHANE cannot be made into a homogeneous liquid. As HYTHANE is cooled below the critical temperature of methane (−260° F.), methane will begin to condense, leaving gaseous residue increasingly rich in hydrogen. There is no significant solubility of hydrogen in liquid methane. However, if HYTHANE is maintained above the critical temperature of methane, the pressure of HYTHANE can be increased to any reasonable pressure with no concern for condensation. Compact containers for this cold high pressure gas are called “supercritical” storage tanks. Like dewars, these tanks are highly insulated. Unlike dewars, the inner vessel is rated for high pressures, (e.g., 1000 psig).
In view of the limitations of conventional alternative fuels and systems, it would be advantageous for an alternative fuel system to have new and different features that overcome some of these limitations. Aside from onboard fuel container issues, the method and equipment for preparing accurately blended HYTHANE and delivering it into the vehicle's onboard tanks at supercritical conditions are important. Cost and reliability of infrastructure are also critical to the success of any alternative fuel technology.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.